The best mycorrhizal fungi for most UK gardeners is a product containing a proven arbuscular mycorrhizal fungus, applied directly where it can contact plant roots — particularly when planting, transplanting or repotting. Mycorrhizal fungi form a natural relationship with plant roots, effectively extending the root network and helping plants access water and mineral nutrients from the surrounding soil or growing medium. Plant Tonics Mycorrhizal Fungi contains Rhizophagus intraradices and is available in 100g, 200g, 400g, 1kg and 2.5kg sizes. Full guide below.

What Are Mycorrhizal Fungi?

Mycorrhizal fungi are beneficial fungi that live in association with plant roots. The word mycorrhiza means fungus-root, describing the relationship between the fungal network and the plant's root system.

The fungi grow alongside or within plant roots and produce microscopic strands called hyphae that extend into the surrounding growing medium.

These fungal strands can effectively increase the area explored by the plant's root system, helping it access water and mineral nutrients beyond the immediate root zone. The RHS describes mycorrhizal fungi as beneficial fungi that can act as an extension to plant roots.

The relationship works both ways: the plant supplies the fungi with sugars, while the fungi help the plant access resources from the soil.

In simple terms:

Plant roots + beneficial fungi = a larger effective root network.

Why Are Mycorrhizal Fungi Important for Plant Roots?

Plant roots naturally explore the soil looking for water and nutrients. Root hairs provide a large absorbent surface area, but the fungal network can extend this reach further into the surrounding growing medium.

That can be particularly useful when plants are establishing in a new environment, such as after planting, transplanting or repotting.

Mycorrhizal fungi are therefore not simply another type of plant fertiliser. They work biologically with the root system rather than simply supplying nutrients.

Key Benefits of Mycorrhizal Fungi

A few things make mycorrhizal fungi useful as part of a root-focused plant care routine:

Root support — beneficial fungi form an association with plant roots and extend into the surrounding growing medium.

Nutrient uptake — fungal hyphae can help plants access mineral nutrients from a greater area of soil.

Water access — the extended fungal network can help plants access water beyond the immediate root zone.

Plant establishment — applying mycorrhizal fungi at planting can support the development of the plant-root relationship.

Soil biology — mycorrhizal fungi form part of the wider biological activity within healthy soil.

Long-term root support — rather than acting as a conventional feed, mycorrhizal fungi work alongside the plant's natural root system.

Mycorrhizal Fungi: At a Glance

Always follow the specific application instructions supplied with the product you purchase.

Plant Tonics Mycorrhizal Fungi

Plant Tonics Mycorrhizal Fungi is designed to support the relationship between plant roots and beneficial soil fungi.

It contains Rhizophagus intraradices, an arbuscular mycorrhizal fungus that forms associations with the roots of many plants.

Rather than functioning as a conventional fertiliser, it is designed to provide natural root support from the ground up, helping establish the biological relationship between plant roots and the surrounding growing medium.

Key features:

• Contains Rhizophagus intraradices

• Beneficial mycorrhizal fungi for plant roots

• Supports nutrient uptake

• Helps extend the effective root network

• Suitable for planting and transplanting

• Suitable for pots and containers

• Suitable for trees and shrubs

• Suitable for flowers, vegetables and fruit plants

• Available in 100g, 200g, 400g, 1kg and 2.5kg sizes

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When Should You Use Mycorrhizal Fungi?

The most straightforward time to use mycorrhizal fungi is when planting or transplanting, because the product can be placed directly where the roots are developing.

This is particularly relevant for:

• New trees and shrubs

• Flowers and perennials

• Bedding plants

• Fruit and vegetable plants

• Houseplants

• Container plants

• Nursery stock

• Repotting

• Transplanting

• Raised beds

• New garden planting

The RHS specifically notes that, on poor soils, mycorrhizal inoculants applied in contact with roots may help trees and shrubs establish.

Can You Use Mycorrhizal Fungi in Pots and Containers?

Yes.

Container-grown plants have a limited volume of growing medium for their roots to explore. The RHS notes that plants in containers have restricted root networks and generally need more feeding and watering than plants growing in open ground.

Mycorrhizal fungi can be incorporated into the growing medium when potting or repotting, helping establish the plant-fungi relationship around the roots.

This makes them particularly useful for:

• Houseplants

• Patio plants

• Container-grown flowers

• Fruit plants

• Vegetable containers

• Herbs

• Young plants

• Newly repotted plants

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Can You Use Mycorrhizal Fungi on Trees and Shrubs?

Yes.

Trees and shrubs develop extensive root systems and establishing healthy roots is an important part of successful planting.

The RHS recommends considering mycorrhizal inoculants when planting trees and shrubs, particularly on poor soils, with the inoculant applied in contact with the roots.

Mycorrhizal fungi can therefore be particularly relevant when planting:

• Ornamental trees

• Fruit trees

• Shrubs

• Roses

• Hedging

• Young trees

• Nursery-grown trees and shrubs

For detailed planting advice, see the RHS Trees and Shrubs: Planting Guide.

Can You Use Mycorrhizal Fungi with Fertiliser?

They are not the same thing and should not be treated as interchangeable.

Fertiliser supplies nutrients, while mycorrhizal fungi form a biological association with plant roots.

The RHS notes that heavily fertilised soils can support fewer mycorrhizal fungi and specifically advises against using phosphorus-rich fertilisers alongside mycorrhizal fungi.

This is an important point when building a plant nutrition routine: more fertiliser is not always better.

For general plant nutrition guidance, see the RHS guide to How Plants Absorb Nutrients.

Can Mycorrhizal Fungi Help with Transplant Shock?

Mycorrhizal fungi can be useful when plants are being planted or transplanted, because this is when the root system is adapting to a new growing environment.

Applying the fungi where they can contact the roots gives the beneficial fungi the opportunity to establish alongside the developing root system.

However, mycorrhizal fungi are not a cure-all for transplant shock. Good planting technique, appropriate watering, suitable soil conditions and correct aftercare remain important.

For trees and shrubs, the RHS highlights root health, weather, soil conditions and aftercare as important considerations when planting.

How to Apply Mycorrhizal Fungi

The most important part of applying mycorrhizal fungi is getting the product close to the roots.

When planting

Apply the recommended amount into the planting hole so the product comes into contact with the roots.

When transplanting

Apply around the root zone when moving the plant into its new growing environment.

When potting or repotting

Mix or apply the product according to the product instructions so it is positioned close to the developing roots.

For established plants

Apply around the root zone according to the manufacturer's instructions.

Always follow the application rate and directions supplied with the specific product.

Common Mycorrhizal Fungi Mistakes to Avoid

Applying it away from the roots

Mycorrhizal fungi work in association with roots, so application should place the product where it can establish contact with the root system.

Treating it as a fertiliser

Mycorrhizal fungi and fertilisers perform different roles. Mycorrhizal fungi support a biological root relationship rather than simply supplying NPK nutrients.

Over-fertilising at the same time

Heavy fertilisation can reduce the need for plants to form mycorrhizal associations, and high nutrient levels can negatively affect beneficial soil microorganisms.

Assuming more is always better

Follow the recommended application rate rather than adding excessive quantities.

Ignoring the growing environment

Mycorrhizal fungi cannot compensate for poor drainage, severe compaction, unsuitable soil, inadequate watering or incorrect planting.

Good root care is about creating the right conditions for the whole root environment.

Mycorrhizal Fungi vs Fertiliser

They are different tools rather than direct alternatives.

A healthy plant care routine may involve supporting the growing medium, roots, soil biology and nutrition rather than relying on fertiliser alone.

Which Plants Can Benefit from Mycorrhizal Fungi?

Mycorrhizal associations occur across a very wide range of plants. The RHS describes mycorrhizas as important to most wild plants and lists almost all plants as potentially affected.

Plant Tonics Mycorrhizal Fungi is suitable for a wide range of garden and growing applications, including:

• Flowers

• Trees

• Shrubs

• Roses

• Bedding plants

• Fruit plants

• Vegetables

• Herbs

• Bulbs

• Perennials

• Houseplants

• Container plants

• Nursery stock

This makes mycorrhizal fungi a versatile addition to a root-focused plant care routine.

What Is Rhizophagus intraradices?

Rhizophagus intraradices is an arbuscular mycorrhizal fungus used to form beneficial associations with plant roots.

Arbuscular mycorrhizal fungi grow within roots and produce fungal hyphae that extend into the surrounding soil. The RHS describes these fungi as forming extensive networks that help absorb water and nutrients.

Plant Tonics Mycorrhizal Fungi uses Rhizophagus intraradices as its mycorrhizal fungus.

This makes it a targeted biological product for gardeners looking to support their plants from the roots up.

How Mycorrhizal Fungi Fit Into a Plant Care Routine

Think of plant care as a complete system rather than a single product.

Healthy soil → Healthy roots → Effective nutrient uptake → Strong plant growth

Mycorrhizal fungi form one part of that system.

Good growing conditions, suitable watering, appropriate nutrition, organic matter and careful planting all remain important.

The RHS also recommends maintaining healthy soil biology by avoiding unnecessary cultivation and excessive fertiliser and fungicide use.

FAQ

What are mycorrhizal fungi?

Mycorrhizal fungi are beneficial fungi that form a relationship with plant roots. Their fungal hyphae extend into the surrounding growing medium and can help plants access water and mineral nutrients beyond the immediate root area.

What are the benefits of mycorrhizal fungi?

Mycorrhizal fungi can support root development, nutrient uptake and plant establishment by forming a beneficial association with plant roots.

Are mycorrhizal fungi good for plant roots?

Yes. They form a natural association with plant roots and can effectively extend the root network through fungal hyphae.

When is the best time to apply mycorrhizal fungi?

Planting, transplanting and repotting are particularly useful times because the fungi can be positioned close to the developing or disturbed root system.

Can I use mycorrhizal fungi in pots?

Yes. Mycorrhizal fungi can be used when potting and repotting container-grown plants, provided the product is suitable for the plant and growing medium.

Can I use mycorrhizal fungi on trees and shrubs?

Yes. Mycorrhizal inoculants can be used when planting trees and shrubs. The RHS notes that applying an inoculant in contact with roots may help establishment, particularly on poor soils.

Can I use mycorrhizal fungi on vegetables and fruit plants?

Mycorrhizal fungi can form associations with many edible plants. Always check the specific product label for its approved uses and application instructions.

Do mycorrhizal fungi replace fertiliser?

No. Mycorrhizal fungi and fertilisers have different functions. Fertilisers provide nutrients, while mycorrhizal fungi support the biological relationship between roots and soil fungi.

Can I use mycorrhizal fungi with fertiliser?

They should not simply be treated as interchangeable products. In particular, the RHS advises avoiding phosphorus-rich fertilisers alongside mycorrhizal fungi because high phosphorus availability can reduce the plant's reliance on the fungal association.

Can mycorrhizal fungi help after transplanting?

They can support the root environment during plant establishment, but successful transplanting also depends on appropriate planting, watering, soil conditions and aftercare.

How much mycorrhizal fungi should I use?

Application rates depend on the product and the situation. Always follow the instructions on the Plant Tonics packaging for the correct amount and application method.

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Plant Tonics is a UK plant nutrition brand developing products for houseplants, orchids, specialist growers, gardens and wider plant care. Mycorrhizal fungi are one part of a healthy root and soil management approach — always follow the specific instructions on the product you use.

Plant Care. Naturally Better.